16 MISC. PUBLICATION 3 4 0, U. S. DEPT. OF AGRICULTURE 



When fumigation is done in cars, more gas is required if the bunkers 

 contain ice than if they do not. 



In addition to the methods just described there is a fourth, de- 

 veloped in recent years, that involves the use of sodium acid sulphite, 

 a compound that releases sulphur dioxide slowly when brought in 

 contact with moist air. Five grams of this chemical, sprinkled in the 

 paper pad used at the bottom of display lugs or mixed with the saw- 

 dust sometimes used as a packing medium, has generally given as 

 satisfactory protection against mold and decay as any one of the other 

 treatments. It is sometimes used in addition to the other treatments. 



If too much of the sulphite is used, or if too much gas is applied in 

 using the commoner fumigation methods, or if such fumigation is 

 continued too long, grapes may be so injured as to seriously impair 

 their market value. If grapes are weak, or immature, or very warm 

 they absorb the gas more readily, and are therefore more likely to be 

 injured by fumigation than if they are firm, mature, or cold. Some 

 varieties take up the gas faster than others and consequently are 

 more easily injured. Fairly resistant varieties are Hibier 9 and 

 Alicante Bouschet; Castiza (Red Malaga) and Emperor are quite 

 susceptible to the injury. 



The injury is caused by the sulphur dioxide which the grapes absorb. 

 It may occur in two fairly distinct forms: (1) A bleaching or decoloriza- 

 tion of the skin of the fruit, usually most pronounced at or near the 

 stem end or around cracks in the skin (sometimes in isolated circular 

 spots) but often extending over the whole surface of the berry (pi. 8, C) ; 

 and (2) a deadening or dulling of the color but without definite bleach- 

 ing. This form of the injury has been observed chiefly in Emperors 

 (pi. 8, A). Grapes severely injured by sulphur dioxide sometimes 

 become wet and sticky because of the killing of the skin and the 

 subsequent leakage of juice. 



If the injury and bleaching occur only in a narrow zone at the stem 

 end, that part of the skin and the underlying flesh may eventually 

 dry out and collapse, thus forming a small depression or cup, which at 

 first might be mistaken for the beginning of decay (pi. 8, B). How- 

 ever, the skin over such a depression is decolorized, not discolored, 

 and there is no odor or taste of decay. The condition described is 

 sometimes referred to as sinking of the cap stems. 



In mild injury the coloring matter of the skin is not destroyed, 

 or so little is destroyed that there is no perceptible color change. 

 In severe injury colored varieties may be bleached and white ones 

 assume a grayish cast. The normal color does not return even though 

 the fruit is removed from the car or other storage space and exposed 

 for several days to the air. Under warm temperatures, injured grapes 

 usually develop a brown or dead color, probably caused by oxidation 

 of injured tissues. Badly injured grapes usually have a distinctly 

 disagreeable, astringent flavor. 



The injury is more likely to occur when the sulphur dioxide is 

 produced by the burning of sulphur than when it is obtained from 

 cylinders of the liquefied gas, because it is much more difficult in the 

 former case to regulate the distribution of the gas around the fruit. 

 Furthermore, the burning of sulphur raises the temperature in the 

 car and this in itself causes the fruit to absorb the gas more rapidly. 



9 See footnote 5, p. 7. 



